In a UMTS (Universal Mobile Telecommunications System) network, the specifications of long-term evolution (LTE) have been drafted for the purposes of further increasing high-speed data rates, providing low delay and so on (non-patent literature 1). In LTE, as multiple access schemes, a scheme that is based on OFDMA (Orthogonal Frequency Division Multiple Access) is used in downlink channels (downlink), and a scheme that is based on SC-FDMA (Single-Carrier Frequency Division Multiple Access) is used in uplink channels (uplink). Also, successor systems of LTE (referred to as, for example, “LTE-advanced” or “LTE enhancement” (hereinafter referred to as “LTE-A”)) have been under study for the purpose of achieving further broad bandization and increased speed beyond LTE, and the specifications have been drafted.
As duplexing methods in radio communication, there are frequency division duplexing (FDD) to divide between the uplink (UL) and the downlink (DL) based on frequency, and time division duplexing (TDD) to divide between the uplink and the downlink based on time. In TDD, the same frequency region is applied to uplink and downlink communication, and signals are transmitted and received to and from one transmitting/receiving point by dividing the uplink and the downlink based on time.
In TDD in the LTE system, a plurality of frame configurations (DL/UL configurations) with different transmission ratios between uplink subframes (UL subframes) and downlink subframes (DL subframes) are defined. To be more specific, as shown in FIG. 1, seven frame configurations, namely DL/UL configurations 0 to 6, are defined, where subframes #0 and #5 are allocated to the downlink and subframe #2 is allocated to the uplink. Also, in TDD, delivery acknowledgement signals (HARQ) in response to the downlink shared channel (PDSCH) that is transmitted in each DL subframe are fed back using predetermined UL subframes, which are determined on a per DL/UL configuration basis.